Tissue factor (TF) is the lipoprotein cofactor for blood coagulation factor VIIa. It is essential for initiation of the "extrinsic" pathway of coagulation and, in addition, may play a critical role in "intrinsic" coagulation as well. Cellular expression of TF has been implicated in the thromboembolic complications which occur "idiopathically" and those associated with infectious, inflammatory, and neoplastic disorders. Small quantities of highly purified human TF have already been isolated in our laboratory. We propose the large scale purification of human TF apoprotein and its biochemical characterization. Specific polyclonal and monoclonal anti-TF antibodies will be raised and immunoassays for TF development. These tools will be used to study the in vitro synthesis of TF by cultured cells focusing on the possible presence of inactive, precursor forms of TF, the determination of the intracellular location of TF, and the mechanism of TF transfer to the cell surface. Normal plasma contains an inhibitor of TF activity which likely plays an important physiological role in the regulation of in vivo hemostasis and may explain the clinical requirement for an intact "intrinsic" coagulation pathway (i.e., the presence of factors VIII and IX). This TF inhibitor will be purified and characterized and its mode of action determined. Polyclonal and monoclonal anti-inhibitor antibodies will be raised and used to construct immunoassays for the TF inhibitor in plasma. Functional and immunoassays for both TF and TF inhibitor will be used to detect their levels in blood from normals and patients with specific disease states. In particular, studies will be performed to assess the interrelationship between TF and TF inhibitor levels in thromboembolic disease. Finally, the location of TF in normal and pathologic tissues will be determined using immuno-histochemical or immuno-fluorescent techniques with specific reference to comparing normal and atherosclerotic vessels. These studies are designed to provide information, now lacking, concerning the initiation and control of coagulation at the TF level and the interrelationship between the classical "extrinsic" and "intrinsic" coagulation pathways in vivo. The results should enhance our understanding of normal hemostasis and pathologic thromboembolism.